Basic Science in Orthopaedics Practice Questions

Q: Which of the following carries a higher risk of DVT and pulmonary thromboembolism?

Hip surgeries. **Explanation:** The risk of Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE) is governed by **Virchow’s Triad**: endothelial injury, stasis, and hypercoagulability. **Hip surgeries** (such as Total Hip Arthroplasty or Hip Fracture surgery) carry one of the highest risks for venous thromboembolism (VTE) in surgical practice. This is due to several factors: 1. **Extensive Tissue Trauma:** Major orthopedic procedures release significant amounts of thromboplastin, inducing a hypercoagulable state. 2. **Venous Stasis:** Post-operative immobilization and the use of tourniquets or intraoperative positioning lead to blood pooling. 3. **Direct Vessel Injury:** Manipulation of the femur can cause direct thermal or mechanical injury to the femoral vein. **Analysis of Incorrect Options:** * **Hand and Breast Surgery:** These are generally considered "low-risk" procedures. They involve shorter operative times, minimal blood loss, and allow for early mobilization, which prevents stasis. * **Obesity:** While obesity is a significant **patient-related risk factor** for DVT, the question asks which option carries a *higher* risk. Major orthopedic surgery (a procedure-related factor) is a much stronger independent trigger for acute VTE than obesity alone. **Clinical Pearls for NEET-PG:** * **Highest Risk Procedures:** Hip arthroplasty, Knee arthroplasty, and Pelvic fractures. * **Prophylaxis:** Low Molecular Weight Heparin (LMWH), Fondaparinux, or Rivaroxaban are standard. Mechanical prophylaxis (IPC pumps) is used as an adjunct. * **Gold Standard Diagnosis:** Contrast Venography (historically), but **Duplex Ultrasonography** is the investigation of choice in clinical practice. * **Fatal PE:** This is the most common cause of sudden death following major orthopedic surgery.

Q: Which line joins the greater trochanter and the anterior superior iliac spine?

Schoemaker's line. **Explanation:** The correct answer is **Schoemaker’s line**. This clinical line is used to assess the position of the greater trochanter in relation to the pelvis, which is vital for diagnosing hip pathologies. **1. Why Schoemaker’s Line is Correct:** Schoemaker’s line is an imaginary line drawn from the tip of the **greater trochanter** through the **Anterior Superior Iliac Spine (ASIS)** and extended toward the midline of the abdomen. * **Normal:** The line passes **above the umbilicus**. * **Abnormal:** If the greater trochanter is displaced proximally (e.g., in femoral neck fractures, developmental dysplasia of the hip, or Perthes disease), the line passes **below the umbilicus**. **2. Analysis of Incorrect Options:** * **Perkin’s Line:** A vertical line drawn downward from the lateral edge of the acetabular roof on a pelvic X-ray. It is used to diagnose Congenital Dislocation of the Hip (CDH); the femoral head should normally lie medial to this line. * **Nélaton’s Line:** A line connecting the **ASIS to the Ischial Tuberosity**. In a normal hip, the greater trochanter lies on or below this line. If the trochanter is felt above this line, it indicates upward hip dislocation or a neck fracture. * **Chiene’s Line:** A line joining the two ASIS and another joining the two greater trochanters. Normally, these lines are parallel. Non-parallelism suggests pelvic tilt or trochanteric displacement. **Clinical Pearls for NEET-PG:** * **Bryant’s Triangle:** Used to measure the upward displacement of the trochanter. The horizontal base of the triangle shortens in hip fractures. * **Trendelenburg Test:** Assesses the stability of the hip and the strength of the abductors (Gluteus medius and minimus). * **Shenton’s Line:** An anatomical curve on X-ray formed by the inferior margin of the femoral neck and the superior margin of the obturator foramen. Interruption indicates hip pathology.

Q: When the gap between fracture segments is between 0.3-1mm, what type of healing occurs?

Woven bone formation later replaced by lamellar bone.. This question tests your understanding of **Primary (Direct) Bone Healing**, which occurs only under conditions of absolute stability (e.g., compression plating). Primary healing is further divided into two types based on the microscopic gap between fracture fragments: **1. Why Option B is Correct (Gap Healing):** When the fracture gap is between **0.1 mm and 1 mm**, it is too wide for direct lamellar growth but stable enough to avoid callus. This is called **Gap Healing**. * Initially, the gap is filled by **woven bone** (formed by osteoblasts depositing bone perpendicular to the long axis). * Subsequently, longitudinal **Haversian remodeling** occurs, where "cutting cones" (osteoclasts followed by osteoblasts) replace the woven bone with permanent **lamellar bone**. **2. Why other options are incorrect:** * **Option A:** Direct lamellar bone formation (Contact Healing) occurs only when the gap is **less than 0.01 mm** and fragments are in direct contact. Here, lamellar bone is formed immediately across the fracture line without a woven bone precursor. * **Option C:** Secondary healing occurs when there is **relative instability** (e.g., intramedullary nailing or casts). It is characterized by **callus formation** and involves a cartilaginous intermediate stage, which is absent in primary gap healing. **High-Yield NEET-PG Pearls:** * **Absolute Stability:** Leads to Primary Healing (No Callus). * **Relative Stability:** Leads to Secondary Healing (Callus present). * **Cutting Cones:** The functional unit of bone remodeling during primary healing. * **Strain Theory (Perren):** Bone formation requires low strain. If the gap is too wide or motion is too high, fibrous tissue or non-union occurs instead of bone.

Q: Which of the following is NOT a characteristic of osteogenesis imperfecta?

Impaired healing of fractures. **Explanation:** **Osteogenesis Imperfecta (OI)**, also known as "Brittle Bone Disease," is a genetic disorder primarily caused by mutations in the **COL1A1 and COL1A2 genes**, leading to a quantitative or qualitative defect in **Type 1 Collagen**. 1. **Why "Impaired healing of fractures" is the correct answer:** Despite the bones being fragile and prone to multiple fractures, the **healing process (callus formation) in OI is generally normal**. In fact, some patients may even exhibit "Hyperplastic Callus" formation (especially in Type V). The defect lies in the structural integrity of the bone matrix, not in the biological capacity of the bone to repair itself. 2. **Analysis of Incorrect Options:** * **Deafness:** This is a classic feature caused by otosclerosis (fixation of stapes) or compression of the auditory nerve due to deformities in the skull bones. * **Laxity of joints:** Since Type 1 collagen is a major component of ligaments and tendons, its deficiency leads to significant ligamentous laxity and joint hypermobility. * **Frequent fractures:** This is the hallmark of the disease. The defective collagen leads to thin, porous cortices and sparse trabeculae, making bones extremely brittle. **High-Yield Clinical Pearls for NEET-PG:** * **Blue Sclera:** The most famous sign; occurs because the thinness of the scleral collagen allows the underlying choroidal veins to show through. * **Sillence Classification:** Used to grade severity (Type I is mildest/most common; Type II is perinatal lethal). * **Wormian Bones:** Multiple small intrasutural bones seen on skull X-rays. * **Treatment:** Bisphosphonates (e.g., Pamidronate) are the medical mainstay to increase bone density; **Sillence (telescoping) nails** are used surgically to manage long bone fractures.

Q: Which part of the bone is the most metabolically active?

Endosteal surface. **Explanation:** The **Endosteal surface** (Endosteum) is the most metabolically active part of the bone. This is primarily because the endosteum lines the inner cavities of the bone (medullary canal and trabeculae), where it remains in direct contact with the highly vascular bone marrow. It contains a high concentration of osteoprogenitor cells, osteoblasts, and osteoclasts, making it the primary site for **bone remodeling** and mineral exchange. **Analysis of Options:** * **Endosteal surface (Correct):** It has the highest rate of turnover. In conditions like hyperparathyroidism, the endosteal surface shows the earliest signs of resorption (subendosteal resorption). * **Cancellous bone (Incorrect):** While cancellous (trabecular) bone is significantly more metabolically active than cortical bone due to its high surface-area-to-volume ratio, the *surface* where the cellular activity actually occurs is the endosteum. * **Cortical bone (Incorrect):** This is the dense, outer shell of the bone. It is primarily structural and has a much slower turnover rate compared to cancellous bone. * **Periosteal surface (Incorrect):** The periosteum is essential for appositional growth and fracture healing (callus formation), but its baseline metabolic turnover is lower than that of the endosteal surface. **NEET-PG High-Yield Pearls:** 1. **Bone Remodeling Units (BRUs):** Remodeling occurs 5–10 times faster in cancellous bone than in cortical bone. 2. **Blood Supply:** The inner 2/3rd of the cortex is supplied by the nutrient artery (centrifugal flow), while the outer 1/3rd is supplied by periosteal vessels. 3. **Endosteal Scalloping:** This is a classic radiological sign seen in intramedullary tumors (like Chondromas) or metabolic bone diseases, reflecting high endosteal activity.

Q: Wading gait is seen in which of the following conditions?

Common peroneal nerve injury. **Explanation:** The correct answer is **Common peroneal nerve injury (Option C)**. **1. Why Common Peroneal Nerve Injury is Correct:** Common peroneal nerve (CPN) injury leads to paralysis of the muscles in the anterior and lateral compartments of the leg, resulting in **Foot Drop**. To prevent the toes from dragging on the ground during the swing phase of walking, the patient must lift the knee higher than normal. This compensatory mechanism is known as a **High Steppage Gait** or **Wading Gait** (resembling someone walking through shallow water). **2. Analysis of Incorrect Options:** * **Bilateral Dislocation of the Hip (Option A):** This condition typically presents with a **Waddling Gait**. Due to the loss of a stable fulcrum and ineffective abductor mechanism (Trendelenburg positive) on both sides, the patient shifts the trunk from side to side. * **Myopathies (Option B):** Proximal muscle weakness (e.g., Duchenne Muscular Dystrophy) also results in a **Waddling Gait** due to weakness of the gluteus medius and maximus. * **Unilateral Dislocation of the Hip (Option D):** This presents with a **Lurching Gait** (Trendelenburg gait) where the trunk tilts toward the affected side during the stance phase to maintain pelvic balance. **3. Clinical Pearls for NEET-PG:** * **Trendelenburg Test:** Positive in conditions with abductor mechanism failure (e.g., Polio, CDH, SCFE). * **Antalgic Gait:** A "pain-relieving" gait characterized by a shortened stance phase on the affected limb. * **Hand-to-Knee Gait:** Seen in **Quadriceps paralysis** (e.g., Polio), where the patient pushes the thigh back to lock the knee in extension. * **Stamping Gait:** Seen in **Sensory Ataxia** (Tabes Dorsalis) due to loss of proprioception.

Q: Which of the following is NOT TRUE regarding the effect of aging on articular cartilage?

Increased production of glycosaminoglycans. **Explanation:** Articular cartilage undergoes specific biochemical and structural changes as a result of physiological aging (senescence), which are distinct from the pathological changes seen in osteoarthritis. **Why Option A is the Correct Answer (The "Not True" Statement):** With aging, the synthetic activity of chondrocytes decreases. There is a **decreased production of glycosaminoglycans (GAGs)** and proteoglycans. Furthermore, the GAG chains produced are shorter in length (specifically a decrease in Chondroitin-6-Sulfate). Therefore, an *increased* production of GAGs is incorrect. **Analysis of Other Options:** * **B & C (Decreased production/Increased degradation):** Aging is characterized by a shift in the metabolic balance where the rate of degradation of the extracellular matrix (ECM) exceeds the rate of synthesis. This leads to a net loss of proteoglycan content. * **D (Decreased water content):** This is a high-yield distinction. In **normal aging**, the water content of articular cartilage **decreases**, leading to reduced elasticity. (Contrast this with **Osteoarthritis**, where water content initially **increases** due to the breakdown of the collagen network). **High-Yield Clinical Pearls for NEET-PG:** * **Chondroitin Sulfate Ratio:** Aging leads to a decrease in the Chondroitin-4-Sulfate to Chondroitin-6-Sulfate ratio (C4S decreases more than C6S). * **Keratan Sulfate:** Unlike GAGs, the concentration of Keratan Sulfate actually **increases** with age. * **Modulus of Elasticity:** Due to decreased water and proteoglycans, the modulus of elasticity decreases, making the cartilage more brittle and prone to fatigue failure. * **Advanced Glycation End-products (AGEs):** Aging increases the non-enzymatic cross-linking of collagen, which turns the cartilage yellowish and increases stiffness.

Question 1

A 5-year-old boy falls off his bike and fractures his humerus. After the bone is set by an emergency room physician, which of the following is responsible for producing the majority of the new bone that will reunite the two fragments?

Accepted Answer

Periosteum

Answer

Cancellous bone

Answer

Cartilage

Answer

Compact bone

Question 2

Which of the following carries a higher risk of DVT and pulmonary thromboembolism?

Accepted Answer

Hip surgeries

Answer

Hand surgery

Answer

Breast surgery

Answer

Obesity

Question 3

Which line joins the greater trochanter and the anterior superior iliac spine?

Accepted Answer

Schoemaker's line

Answer

Perkin's line

Answer

Nelton's line

Answer

Chiene's line

Question 4

Which one of the following definitions best fits the term enthesitis?

Accepted Answer

Inflammation at the site of tendinous or ligamentous insertion into bone

Answer

Inflammation of the periarticular membrane lining the joint capsule

Answer

Inflammation of a sac-like cavity near a joint that decreases friction

Answer

All of the above

Question 5

What is the perichondrial ring?

Accepted Answer

Seen around the epiphyseal plate

Answer

Seen around the foramen magnum

Answer

More prominent in adults

Answer

Shear strength increases with age

Question 6

When the gap between fracture segments is between 0.3-1mm, what type of healing occurs?

Accepted Answer

Woven bone formation later replaced by lamellar bone.

Answer

Direct lamellar bone formation.

Answer

Secondary healing.

Answer

Any of the above.

Question 7

Which of the following is NOT a characteristic of osteogenesis imperfecta?

Accepted Answer

Impaired healing of fractures

Answer

Deafness

Answer

Laxity of joints

Answer

Frequent fractures

Question 8

Which part of the bone is the most metabolically active?

Accepted Answer

Endosteal surface

Answer

Cortical bone

Answer

Cancellous bone

Answer

Periosteal surface

Question 9

Wading gait is seen in which of the following conditions?

Accepted Answer

Common peroneal nerve injury

Answer

Bilateral dislocation of hip

Answer

Myopathies

Answer

Unilateral dislocation of the hip

Question 10

Which of the following is NOT TRUE regarding the effect of aging on articular cartilage?

Accepted Answer

Increased production of glycosaminoglycans

Answer

Decreased production of glycosaminoglycans

Answer

Increased degradation of glycosaminoglycans

Answer

Decreased water content

Basic Science in Orthopaedics — MCQs

Basic Science in Orthopaedics — MCQs

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